Do monkeys play fair? Staging an ultimatum game in the ultimate social primate

Every now and then, my roommate will lean in the frame of my door and pose a simple scenario: “Will you mop the floors if I wash the dishes?” I usually respond positively to the ultimatum (I really can’t stand doing dishes), and when the moment is right, put on some Enya and graciously clean the granite floors of our apartment.

Humans are pretty adept at this type of cooperation. We’ve been doing it for centuries, and most anthropologists agree that cooperation is one of the building blocks that allowed us to develop into more complex societies. Knowing that this seemingly fair trade-off has worked well for me in the past, I almost always keep my promise. If I didn’t, my roommate could easily sanction me by refusing to do the dishes, or by offering an unfair trade next time. Yet, we’re both pretty happy with this setup, and our cooperation ensues.

Now, for the sake of evolutionary argument, let’s say that my roommate and I are not full-grown homo sapiens but rather some other species of primate. Would monkeys, bred in the harsh wild, cooperate in the same manner?

Actually, they probably would. In two separate studies, one by Brosnan & de Waal (2003) and a second by Proctor et al. (2013), both capuchins and chimpanzees tend to cooperate when faced with a similar type of ultimatum game. Rhesus macaques, the most common primate model in neuroscience, are ruthless creatures; there’s no point in trying to get them to act altruistically (though maybe someone will prove me wrong).

Recently, the extremely social marmoset has stepped onto the stage as a contender in neuroscience’s next top model, opening a realm of possibilities for research into social communication and behavior. Unlike macaques, marmosets breed in captivity, can be housed together, and have the potential for transgenic lines such as those in mice. In addition, their brains don’t have bumps and grooves like macaque (or human) brains, making it very easy to stick an electrode in and know exactly where you’re recording. Cory Miller at UCSD has exploited their stereotyped social calls as a way to study the auditory system, but their proclitivity for social cooperation on a decision-making task is a completely open question.

This open question is the one I tackled in my second-year qualifying exam, in which I proposed a three part approach to understanding social cooperation in marmosets: train them on a modified ultimatum game task, record from areas such as the orbitofrontal cortex that likely encode cooperative behavior, and finally, manipulate these circuits using optogenetics. Using the marmoset to answer such complex questions about human behavior may allow us to manipulate specific cell types and circuits involved in cooperation. Ultimately, we can start to unravel the underpinnings of things like psychopathy, where these cooperative circuits in the brain are likely very weak. So there you go interwebs, a perfectly good study that someone should probably do. In the meantime, I’ll be mopping the floor.

Ashley Juavinett is a second-year PhD student in the Callaway Lab at the Salk Institute. She uses in vivo techniques to understand the neural circuitry underlying visual perception in mice. @ashleyjthinks